Vol.59-] A EOWEK-GKEENSAND F0SSILIFEK0TTS BAND. 241 



among which brachiopods and other shells, with the tests converted 

 into limonite and well-preserved, are sometimes embedded. From 

 their size and character, it is clear that the larger fragments of this 

 breccia cannot have been transported far. The iron-pan floor 

 underlying these patches of breccia is polished and worn into little 

 hollows, as though by the drifting of the overlying rubble and sand 

 across it ; and some large blocks on the tip-heap of Rigby Harris's 

 Pit, apparently from this horizon, were encrusted on their 

 worn irregular surfaces by adherent oysters and 

 Serpulce, clearly proving that the rock-band from which 

 they came had constituted for a time the actual 

 sea-floor. 



It is scarcely likely that the sand could undergo cementation and 

 induration at the surface immediately in contact with the sea-water. 

 More probably the action took place at some little depth within the 

 deposit, the hardened band being afterwards laid bare by currents 

 of increased strength, which winnowed away all the loose material 

 overlying it at this particular spot, until further erosion was checked 

 by its presence. The fragments of iron-grit in the breccia, if not 

 derived from portions of the same floor, may represent the remnants 

 of impersistent masses which had formed at slightly higher levels 

 and were let down piecemeal by the removal of their matrix. 

 Obscure markings, suggestive of the almost obliterated casts of 

 organisms, are frequently visible in this band of iron-grit ; but it has 

 yielded no fossil of which the nature could be definitely identified. 



The persistent iron-pan floor which occurs above the fossiliferous 

 belt and is directly overlain by the Gault-Clay, is of a character 

 similar to that below the belt. It shows the same curiously- 

 corrugated surface, and contains the same abundance of polished 

 grit-grains. Indeed, the two occasionally come almost in contact 

 with each other (as shown in fig. 3, p. 238), thus apparently 

 marking off the intervening band into huge lenticles. During one 

 of our visits to the section, the surface of the floor immediately 

 underlying the Gault was freshly exposed in one part of the 

 excavations over an area of several square yards, and exhibited a 

 smooth-worn appearance, as though it had suffered attrition before 

 the Gault-Clay was laid down upon it. The preservation of the 

 fossiliferous limestone-lenticles is probably due to the protection 

 afforded by these impervious iron-pan layers, which have shielded 

 the bed between them from the solvent action of percolating waters. 



The Lenticles of Fossiliferous Limestone. 



The fossiliferous masses themselves present in their structure 

 many points of interest. They vary from 2 or 3 to 10 feet or 

 more in length, with a thickness never exceeding 2 feet and 

 generally less. In the interior they are usually of very compact and 

 horny texture, sometimes of a pale flesh-pink colour and sometimes 

 yellowish, but they show every gradation between almost pure 

 limestone and slightly calcareous grit. They are sprinkled through- 



